When it comes to cravings, some women can desire some really out-there things. Ice cream and pickles? Sure. But, coal and sponges? A British study in 2008 found that 31 percent of pregnant women there experienced pica, a craving of nonfood items, including mud, matches, soap, toothpaste and rubber, the BBC reported.

Pica is sometimes blamed on hormonal changes or lack of certain nutrients, such as iron or calcium, but often the origin is a mystery. The study also found that prenatal food cravings in general have doubled in the past 10 years. Researchers said the increase can be "attributed to the fact that modern mums are more assertive in asking for what they want than their older counterparts, who perhaps felt ashamed of their more unusual cravings."